Due to the complexity of this single topic,
I will sub-devide the answer in the (hopefully) correct order.
Foreigners office (Ausländerbehörde) :
Aufenthaltsgesetz (2018) §51(7)
Regulates what happens if you leave the country for a long period of time
- longer than 6 months
- a longer period than agreed with the Ausländerbehörde
the granted leave (Aufenthaltstitel) will be invalidated (erlischt)
If it is your intention to return, you must notify them of the expected date of return which will replace the default 6 months if granted.
There are many different conditions based on what type of titel you have.
- will, upon exit be invalidated when the intention is solely for further educational purposes
- there are other conditions where it will be granted
- permission may be granted based on application
Ausländerbehörde Berlin (in German) :
other states may have slightly different regulations.
The statements above (and below) are based on Berlin from the link above.
Here care must be made to get this right,
so I would make an appointment to clarify the situation.
Registry office (Meldebehörde)
You must only de-register if you are permanently leaving.
- for a temporary foreign trip (sample on the site is for studying) a de-registeration is not needed when the flat is maintained and you have the intention to return
Again, this may differ state by state.
When leaving the country, you must de-register the flat, scan in the de-register confirmation and fill out the form that starts at the link below.
- 'ich dauerhaft ins Ausland ziehe'
should be the second button shown.
- jpg, png, tif and pdf are accepted formats
If you are retaining the flat during yot trip abroad, you must still pay the fees.
If you are subletting the flat, those renting the flat must register themself at the flat using your number as a reference.
Since this fee is household based, they will not have to pay anything extra.
Contract with the employer
As with all contracts (including the rental), you enter into obligations that must be fulfilled.
If both sides agree, anything can be arranged as needed.
So you must contact them and come to an agreement
(Which should be considered a precondition for everything else)
You must check your contract for how much notice (Kündigungsfrist) is needed if you intend to give up the flat.
Also, when you wish to retain the flat, a sub-letting is an alternative.
Most contracts will not allow this.
So you must ask them to agree to an one time exception.
If both sides agree...
If they agree, assume that you will be held responsible to them for any damages your rentees may cause.
You may sign the registration form (as Landlord) of your rentees.
There may be default rent contract forms for sub renting (Untermiete) .
Make sure that electricity, gas counters are noted.
It will be up to you how they pay for the usage, since you will continue the main payments.
There may be organizations that can 'automate' the procces.
If you are retaining, but not sub-renting the flat
Contact your Hauswart (caretaker) and inform them of the timeframe.
Many people deposit their key with the Hauswart in case of lost, forgotten key or cases when absent someone needs to enter the flat (Waterpipe breaks etc.)
They will tell you how to turn off the water main, electricity, heaters to avoid problems and costs.
Often they are helpfull in turning everything back on at the date of expected arrival ...
... and mayby even filling up your refrigerator with some minimal necessities ...
which may not be the first thing you want to do after a long trip.
Pension and health insurance (Krankenkasse)
Whether temporary or permanent nothing needs to be done.
The Health card may not be used during this time, of course.
When you are not working, no payments will be made to both of them.
Depending of the Krankenkasse, you make a contract for insurance for your training in the US.
When you return from the US and again start working apply for a Kontenklärung about 2 months later.
You will have a 'Fehlzeit' for the period in the US. Send proof of your training to them. This will be added to your account and reduce the the waiting time to be eligible for a pension.
If you are younger than 28, this may even increase your pension amount. This is true for any schooling between 17 and 27.
Based on your contract conditions, you must fulfill any conditions contained in the contract.
When moving or otherwise leaving a flat, send a letter to any electricity / Gas company informing them that you are leaving or moving with the following information
- customer number
- meter number and counter (previous and at new address)
- new address
a photo of the meters may assist as proof of the meters values when leaving and found when moving in
You should inform them that you will be away for a specific time so that no post should be sent.
Avoid, during your stay in the US, in becoming a 'US Person'!
- FATCA information can be found on this forum and elsewhere
If this happens you will become, in the eyes of any Bank,
a 'financial toxic waste'.
It is possible your bank will close your account and others refuse to open a new one.
Effects in citizenship waiting time
The site states 'continuance' (Ununterbrochener) residence.
It used to be, but may no longer be, that certain exceptions were made where by only 50% of that time was added.
(I will sniffle around and see if I can find something)
Vorläufige Anwendungshinweise of 2015-07-01
(temporary instuction on how the citizenship laws should be implemented)
states (18.104.22.168) that after an interruption of residence, a maximum of 5 years may be recognized.
So you must assume that this interuption will have a effect and that it will be left to the discretion of the official of what and how this will be handled.
May, again, differ between each state.
no doubt something has been forgotten or needs correction ...